Automatic flash control device for photographic cameras



NOV. 1966 u'rc soN, JR 3,282,180

AUTOMATIC FLASH CONTROL DEVICE FOR PHOTOGRAPHIC CAMERAS Original FiledAug. 6, 1962 FIG '2 MILLER R- HUTCHISON, JR- 36 INVENTOR. 26 28 I BY 5skm W H AT TORNE Y5 United States Patent "ice 3,282,180 AUTOMATIC FLASHCONTROL DEVICE FOR PHOTOGRAPHIC CAMERAS Miller R. Hutehison, In,Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey ()riginal application Aug. 6, 1962, Ser.- No.215,044. Divided and this application June 29, 1964, Ser. No. 378,848

Claims priority, application Great Britain, June 14, 1962,

2 Claims. (Cl. 95-11) .The present invention relates to photographiccameras and more particularly concerns automatic flashcontrol systemsfor such cameras. This application is a divisional application of US.application Serial No. 215,044, filed August 6, 1962, now abandoned.

In cameras it has long been customary to employ photoflash lamps, timedwith the camera shutters, to illuminate photographic subjects when scenebrightness is low. The use of such photoflash lamps has given rise toseveral problems, the primary one being that the camera operator has hadto make some determination of the necessity for flash operation.

With the advent of photoelectrically controlled exposure systems, itbecame a common practice to provide a camera with a viewfinder signal toindicate visually when the subject illumination is too low for normalphotography and that flash operation is required for proper exposure.Nevertheless the problems of flash operation were still not ended. Whenthe camera operator aims the camera he naturally wants to take a pictureat that time. When he is apprised even by an automatic signal that flashoperation is required, he must make any necessary adjustments of thecamera for flash operation, e.g., coupling the diaphragm adjustment tothe focus adjustment, manually setting the diaphragm and shutter, and ofcourse inserting a flashlamp into the camera. By the time suchadjustments have been made, and assuming that the photographer has thenecessary flashlamp within convenient access, quite often the subjectbrightness has changed or the event to he recorded has transpired. It isthen prudent for the photographer to remove the flashlamp from thecamera unless he intends to next picture to be taken under flashconditions.

The above operation is entirely unsatisfactory and tends to discouragephotography. It leads to waste of film when the photographer eitherforgets to insert a flashlamp or tires, without one, to photograph arelatively dark, transient event. -It leads to waste of flashlamps, andpossible overexposure of a subsequent picture when the photographerforgets to remove an unused flashlamp from the camera after anunsuccessful attempt to readjust the camera for flash operation beforean event has transpired.

It is therefore a primary object of the present invention to control theoperation of a flash bulb in a camera automatically, without anyattention by or knowledge of the camera operator, such that flashoperation will occur when scene brightness is at a low enough level torequire it, but will not occur otherwise.

A further object of the invention is to permit a flashlamp to be carriedin a-camera socket at all times and automatically to prevent itsignition except during low levels of field brightness.

Another object of the invention is to control the flash operation of acamera photoelectrically.

relays, such as the systems illustrated in copending application SerialNo. 191,977, filed May 2, 1962, and now abandoned in favor of continuingapplication Serial No. 265,635, filed March 18, 1963.

Other objects and advantages of the invention will appear from thefollowing description, reference being made to the accompanyingdrawings, wherein:

FIG. 1 is a partial perspective view of a camera showing the elements ofthe present invention and the camera elements cooperating therewith; and

FIG. 2 is a schematic wiring diagram of the invention as described.

Referring to FIGS. 1 and 2, a camera embodying the present invention hasan optical axis 10 on which are located the usual exposure aperture 12and shutter blade 14. A camera actuating member 16 operates the shutterin a well known manner. A viewfinder 18 may be located on a secondoptical axis 19.

A flash bulb 20 is mounted in front of a reflector 22. The flash lamp 20is in a series circuit with a source of electrical potential such asbattery 24 and with a normally open line switch 26 that prevents thebattery 24 from being discharged when the camera is not in use. Theusual shutter timing switch 28 is also in series circuit with the flashbulb 20, as is a flash lamp control switch 58, biased to its closedcondition or position by a spring 60. Connected in parallel with theflash bulb 2t), switch 58 and shutter synchronizing switch 28 is a lightdependent photoresistive'device 36, such as a cadmium sulfide cell, andan electromagnetic relay coil 54 operatively controlling switch 58. Thelight dependent resist-or or photocell 36 is disposed for illuminationby scene light and'for convenience may be located in the viewfinder asillustrated in FIG. 1. Battery 24 is in the circuit with such polaritythat its negative terminal is connected to the terminal of cell 36opposite relay coil 54.

A normally closed relay control switch 56 is connected in parallel withphotocell 36 and permits relay 54 to be fully energized when line switch26 is closed, regardless of field brightness. Control switch 56 is thenopened to connect photocell 36 into the relay circuit, thereaftercontrolling the realy energization as a function of field brightness. Iffield brightness is above a predetermined value, a considerable currentflows through cell 36, energizing relay 54 sufliciently to hold thenormally closed lamp control switch 58 in an open condition against theten sion of spring 60, thereby disabling the lamp firing circuit. Iffield brightness is low, the resistance of photocell 36 is high andrelay energization is too low to hold open the switch 58. In this statethe lamp 20 is fired when shutter synchronizing switch 28 is closed.

In operation, the shorting switch 56 is manually opened to connect thephotocell 36 into the relay circuit. When the camera actuating member 16is moved in the direction shown by the arrow in FIG. 1, it first closesline switch 26 and then operates the shutter in a known manner, which inturn closes the shuttersynchronizing switch 28. If at this time thescene brightness is sufliciently high, the resistance of cell 36 isrelatively low, thereby permitting sufficient current to flow throughthe relay coil 54 and energizing the relay sufliciently to hold' switch58 open to disable the lamp firing circuit. If, however, scenebrightness is below a predetermined level, the resistance of cell 36 isabove a corresponding level,

and relay energization is too low to hold switch 58 open..

Consequently, lamp 20 is fired automatically when shutter synchronizingswitch 28 is closed.

From the foregoing it will be seen that the operation of the flash bulbis completely automatic and requires no attention from the cameraoperator, nor need the camera operator be aware of the conditionsrequiring flash operation.

particular reference to the preferred embodiment shown, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit of the invention and the scope of thesubjoined claims. I claim:

1. In a camera adapted to receive a flash lamp, the combinationcomprising:

means to electrically receive a flash lamp, a source ofelectrical'potential and a switching means in series with said lampreceiving means;

a shutter synchronizing switch in series with said flash lamp receivingmeans to close the flash lamp receiving means circuit in timedrelationship with operation of a shutter;

a photoresistive cell illuminatable by field light and in parallelelectrically with said flash lamp receiving means;

an electromagnetic relay in series electrically with said photoresistivecell and in parallel with said flash lamp receiving meansand saidswitching means;

spring means urging the switching means to a closed position to enablefiring of a-flashlamp in the receiving means, the relay overcoming saidspring means to maintain the switching means in an open condition andprevent firing only when said relay is energized above a predeterminedlevel whenever the resistance in said photoresistive cell is below apredetermined level as determined by field light; and

shorting switch means in parallel with said photoresistive cell topermit said source to energize the relay and maintain the switchingmeans in an open condition independently of the photoresistive cell.

2. In a photographic camera adapted to receive a flashlamp, anautomatically controlled flash lamp firing circuit comprising:

means to electrically receive a flashlamp;

means to receive a source of electrical potential in serieselectricallywith said lamp receiving means to fire a flash lamp in the lampreceiving means;

a lamp control switch in series electrically with said source ofelectrical potential and said lamp receiving means, the lamp controlswitch having an open condition disabling the firing circuit and aclosed condition to enable flash lamp firing;

spring means normally biasing the lamp control switch to the closedposition;

a photoresistive device disposed for illumination by ambient field lightand connected in parallel electrically with said lamp receiving meansand said lamp 7 control switch;

an electromagnetic relay operatively controlling the lamp control switchand connected in series electrically with said photoresistive device andin parallel electrically with said lamp receiving means and said lampcontrol switch, the photoresistive device controlling energization ofthe relay as a function of field brightness, in which the relay isenergized to (a) hold the lamp control switch in the open conditionagainst the bias of the spring means to disable the firing circuit whenthe ambient field light is above a predetermined level, and (b) topermit the spring means to hold the lamp control circuit in the closedcondition to enable lamp firing when ambient field light is below thepredetermined level.

References Cited by the Examiner UNITED STATES PATENTS JOHN M. HORAN,Primary Examiner.

1. IN A CAMERA ADAPTED TO RECEIVE A FLASH LAMP, THE COMBINATIONCOMPRISING: MEANS TO ELECTRICALLY RECEIVE A FLASH LAMP, A SOURCE OFELECTRICAL POTENTIAL AND A SWITCHING MEANS IN SERIES WITH SAID LAMPRECEIVING MEANS; A SHUTTER SYNCHRONIZING SWITCH IN SERIES WITH SAIDFLASH LAMP RECEIVING MEANS TO CLOSE THE FLASH LAMP RECEIVING MEANS INTIMED RELATIONSHIP WITH OPERATION OF A SHUTTER; A PHOTORESISTIVE CELLILLUMINATABLE BY FIELD LIGHT AND IN PARALLEL ELECTRICALLY WITH SAIDFLASH LAMP RECEIVING MEANS; AN ELECTROMAGNETIC RELAY IN SERIESELECTRICALLY WITH SAID PHOTORESISTIVE CELL AND IN PARALLEL WITH SAIDFLASH LAMP RECEIVING MEANS AND SAID SWITCHING MEANS; SPRING MEANS URGINGTHE SWITCHING MEANS TO A CLOSED POSITION TO ENABLE FIRING OF A FLASHLAMPIN THE RECEIVING MEANS, THE RELAY OVERCOMING SAID SPRING MEANS TOMAINTAIN THE SWITCHING MEANS IN AN OPEN CONDITION AND PREVENT FIRINGONLY WHEN SAID RELAY IS ENERGIZED ABOVE A PREDETERMINED LEVEL WHENEVERTHE